text:
What can disqualify an airport to be used as an alternate?
As a military pilot, our regulations listed things that disqualified airports as being alternates.  I have not been able to find a reference to these same items listed in the 14 CFR Part 91.  Does anyone know where to find the regulatory references for the list of things that disqualify an airport as an alternate for an IFR plan?  For example, an airport cannot be used as an alternate if the instrument approach at the airport you plan to use is listed as "Radar Required."  Is that a consideration in General Aviation?  Likewise, I was trained that if a navaid is unmonitored or if the airfield only has GPS approaches, again disqualifies the airfield as an alternate.  However, I don't know where that is written in the FARs.  Does anyone know where I should look?

Possible duplicate of What are "Alternate Minimums"?

There are part 91 rules, 121 rules, and 135 rules for alternate requirements.  Are you asking for non-commercial (91), scheduled carriers (121), or charter (135)?

I was thinking part 91, but the more I research this topic, I'm beginning to think that I'm suffering from "negative transfer."  It looks like I've brought something from my military training that doesn't necessarily apply to Part 91 operations.

As far as Part 91 ops go, paragraph 91.169 is the only IFR alternate requirement to my knowledge.
*Unless otherwise authorized by the Administrator, no person may include an alternate airport in an IFR flight plan unless appropriate weather reports or weather forecasts, or a combination of them, indicate that, at the estimated time of arrival at the alternate airport, the ceiling and visibility at that airport will be at or above the following weather minima:
(1) If an instrument approach procedure has been published in part 97 of this chapter, or a special instrument approach procedure has been issued by the Administrator to the operator, for that airport, the following minima:
(i) For aircraft other than helicopters: The alternate airport minima specified in that procedure, or if none are specified the following standard approach minima:
(A) For a precision approach procedure. Ceiling 600 feet and visibility 2 statute miles.
(B) For a nonprecision approach procedure. Ceiling 800 feet and visibility 2 statute miles.
(ii) For helicopters: Ceiling 200 feet above the minimum for the approach to be flown, and visibility at least 1 statute mile but never less than the minimum visibility for the approach to be flown, and
(2) If no instrument approach procedure has been published in part 97 of this chapter and no special instrument approach procedure has been issued by the Administrator to the operator, for the alternate airport, the ceiling and visibility minima are those allowing descent from the MEA, approach, and landing under basic VFR.*
**If you look in the front of the approach book (DOD or JEPP) it will list the 600/800' limitation for alternate designation.  I guess it's not in the UPT syllabus because the 11-214 (and the DOD for that matter) doesn't honor that specific alternate limitation.  FAR Part 135/121 ops might list other limitations that look like the "RVSM reqd, Wx reporting, GPS only, etc.)
-the queep monster....**

Thanks I've considered all of those possibilities.  In addition to 91.169 which you've included, I've research Part 97, Order 8260.3C (TERPS rules), the Instrument Flying Handbook, Aeronautical Information Manual, and several CFIs with YouTube channels.  None of which I've seen in the  Part 91 side ever goes into these disqualifying items.  It appears to me that the main reference for the A/NA as a disqualifier is in the legend for terminal procedure charts.  Again, I think I brought something over from my military training that doesn't apply to Part 91.  Regardless, thank you for your help.


text:
How is a lead acid battery and a Ni-Cd battery charged on an aircraft?
How is a lead acid battery and a Ni-Cd battery charged on an aircraft, such as an A320?
Is it constant current or voltage?

You may specify which battery(ies) your are talking about.

Related, battery for A320 family.

Constant-voltage, but there's more going on.
Batteries prefer a mildly complex charging curve, because both lead-acid and NiCd charge efficiently in their mid-cycle (20-80%) -- but inefficiently at the top of their range (80-100%).  In a perfect world, a charger pushes them heavily (constant-current) in their midrange, but tapers off for the top-up charge.  The state-of-the-art in lead-acid is 3-stage charging.
If power is pushed into a battery when it should not, the battery will produce a lot of heat, "boil off" water excessively, partly splitting water into hydrogen and oxygen, carry battery acid (or alkaline in the case of NiCd) into the battery box, and shorten the life of the battery pack, especially with lead-acid which already has a short life.
It would be neat if battery voltage and impedance behaved such that constant-voltage charging caused the correct charging curve passively.  No such luck.
Constant-voltage charging is a compromise - the same one cars make - since the charging system is both charging the battery and powering the airplane. The voltage is chosen for least damage/heat/boil-off/hydrogen, at the trade-off of slower charging than a dedicated smart charger.
If the battery is lead-acid and you have depleted it, recharge it ASAP, as it shortens the life of lead-acid batteries to be stored partially discharged.  That won't faze a nickel-cadmium set, they are highly resilient and long-lived.

Airliners like the Airbus A320 use Nickel Cadmium batteries; in case of A320, a pair of main batteries with 23 Ah capacity is used.
While on the aircraft, the batteries are charged using a constant voltage method. As this article notes:

... are "constant-voltage chargers" that apply a fixed voltage to the battery as it charges, similar to what the aircraft electrical system does in flight. With a constant-voltage charger, the charging current starts out relatively high and gradually tapers down toward zero as the battery becomes fully charged.

FAA Aircraft Electrical System Handbook also notes:

The battery charging system in an airplane is of the constant
  voltage type.

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text:
What materials are used to build a military runway?
What type of matrix should be used on a military runway used by C130 aircraft?

Asphalt, concrete, dirt, sand, snow, ice... C-130 is pretty versatile.

Same as the one you use for civilian runway. Military does not change the physics.

Related: https://aviation.stackexchange.com/questions/19313/how-heavy-is-too-heavy-to-land-on-a-grass-strip/19335#19335

@vasin1987 Military aircraft are more commonly designed to deal with less-improved runways than civilian aircraft, especially in the case of military transport aircraft, which are frequently designed to be able to land on and take off from makeshift grass strips in the middle of a war zone or ice fields in Greenland or Antarctica.

I believe C-130 was designed to be operated from unprepared runways for takeoffs and landings. One of the reasons for India to buy it and deploy it to forward operating base.

Depends. Dirt runways can be prepared through dust control by water.
Diego Garcia has been at least since the seventies had the coral reefs mined for aggregate.
Keep in mind that the matrix doesn't have to be high quality, it just has to last until the anticipated end of the war without excessive maintenance costs.

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text:
How to encode an altitude in ARINC429?
How can I encode an altitude (ft) in ARINC429? I didn't understand if I just need to transform it in binary number and then use the "Bipolar Return-to-Zero".
Like for example with an altitude of 25 000 ft.

Which A429 label are you asking about?  there are numerous 'altitude' labels with different coding (BCD, BNR), different ranges, and different resolutions. It also depends on what equipment is the source of the data (equipment code).

I just need examples for some of them. Cause I don't need to know specifically. So you can choose the labels and equipment code you want for both BCD and BNR codings. In this way I will have a better understanding. Thank you very much!

Bipoloar Return to Zero is related to actually transmitting the label. It does not affect the encoding of the label. What device are you trying to transmit from?

From ARINC 429, Attachment 6:

Label 025, Selected Altitude (BCD)
  Five binary coded decimals.  Range is up to 50000.  Resolution is 1
  foot.
Bit 29 (MSC) ------------------------------ Bit 11 (LSC)
  4 2 1 | 8 4 2 1 | 8 4 2 1 | 8 4 2 1 | 8 4 2 1
1 0 0 | 0 0 0 1 | 0 0 0 0 | 0 0 0 0 | 0 0 0 0
  The above line codes to 41000 ft.
  Note: Negative sign is annunciated in the sign/status matrix.
Label 102, Selected Altitude (BNR)
  16 bits of data. Range of 65536. Resolution (value of LSB) is 1 foot.
Bit 28 (MSB)------------------- Bit 13 (LSB) (Bits 12-11 are set to 0)
     1 0 1 0 0 0 0 0 0 0 1 0 1 0 0 0
The above line codes to 41000 ft.
Note: Negative values are encoded as the two’s complements of positive
  values and the negative sign is annunciated in the sign/status matrix.

Perfect! Thank you very much Gerry!

@HariSeldon it is important to note that this only works for those labels. Labels 203 and 204 (for equipment IDs 006,038) use 17 bits of data for a range of 131072 ft with a resolution of 1 ft. It is important to know what Equipment ID is transmitting the value, and for what label


text:
What would be the potential effects of not having an accumulator in the hydraulic system?
In an aircraft, what would be the potential effect of not having an accumulator in the hydraulic system?

Accumulators act as storage for flow. At times of peak flow demand, the accumulator delivers a large flow supply at nominal pressure until its oil has been used up, after which the maximum flow is the pump flow. The same functionality that a capacitor or a battery has in an electric system.
If there are no accumulators installed:

Peak hydraulic power is greatly reduced: peak flow supply equals the pump flow, and pressure drops when the pump supplies high flow.
Pressure surges are high when the pump is running and demand suddenly stops, the accumulator evens out the pressure peak, again like how a capacitor functions. (From @Gerry comment).

They also absorb pressure spikes when the pumps are running and demand suddenly drops, just as a capacitor will absorb a current surge.

Thx, have added.

I think I read about it somewhere that the vibration from the pump that travels in the form of vibrating pressure has caused failures on the pipe on a test aircraft prototype. IIRC that should be XB-70 AV1.


text:
What would be a technical or slang term for 'in the air'?
I'm writing a sci-fi story involving aircraft and space craft. I'm struggling to get the terminology right for referring to a pilot being 'in the air' either on a mission or a training exercise. I have a feeling there is a phrase for this but I'm struggling to think of it.
The context would be military, as in the following sentence:

She kept the Squadron Leader updated as much as she needed to, but she preferred to keep comms chatter to a minimum when she was in the air.

Related: A phrase pilots (may) say to another, instead of "good luck, is "Blue side up!".

Make a cool one up! Slipped? (As in "surly bonds of Earth".) Uber-terra? Litho-detached? (Inspired by a Kerbal Space Program player referring to "Litho-braking".) "Maintaining an air gap"? "Saving Daisies"? "Saving on tyre wear"?

@GrimmTheOpiner: Haha, yes! 'Saving on tyre wear' is a great one.

She kept the Squadron Leader updated as much as she needed to, but she
preferred to keep comms chatter to a minimum when she was...

Military-related terms:

...on patrol
...on station
...on a sortie
...on a shout [British English, specifically used for search and rescue]
...on recce/on recon [British and American English, respectively]

General terms:

...in the air
...airborne
...at the controls
...flying
...in flight
...on a mission
...doing (her) rounds
...aloft
...wheels up

There might be other, more technical terms in use in the military for specific operations or missions but I have no experience there.

If I may offer a suggestion: aloft

@nexus_2006 That's a good suggestion, I've made this a community wiki answer so that other people can add them directly.

Most of those terms refer to being in the air for a specific purpose, or doing something specific while in the air. They're not appropriate for simply saying that someone is in the air.

Aloft is the first word that comes to mind for me, but the problem I see with aloft, as well as "in the air", "airborne", and to a lesser extent "flying" is that these are things that occur in the atmosphere. The OP is looking for a word that satisfies both "flying" in atmosphere and in space. Perhaps "piloting", as in "...when she is piloting her ship."

I've used the term "wheels up" before.

This usually refers to the specific moment of take off. "Wheels up at 0745"

So long as it is not accompanied by shiny-side-down!

Since you've had many in-atmosphere answers, here are a few for not-in-atmosphere flight:

In / On orbit
Weightless
Parabolic (Usually used to say that something is above the Karman line but has not achieved orbital velocity)
Off-planet

There's also exoatmospheric which literally means not-in-atmosphere.

why parabolic, surely that would be an elliptical sub-orbital trajectory?

@jk I guess a segment of an ellipse looks approximately like a parabola. If you throw a baseball (or a fire a canon) at ground level under ideal (e.g. airless) conditions, the trajectory above the ground looks like a parabola though it's, more accurately, a segment of an ellipse. What makes the difference (between a parabola and an ellipse) is whether you travel far enough for the direction of gravity to change.

@jk. It seems that sub-orbital trajectories often encounter a large nickel and iron obstacle which prevents them from completing an ellipse.

@ChrisW yes they look parabolic because the  earth is locally 'flat', if you are getting up to Karman line then you are probably moving enough that earths curvature is important. I just though it was a bit odd cos at that scale you can have a parabolic trajectory but it has the opposite meaning in that it actually escapes. I guess jargon doesn't necessarily have to make sense though

Mostly when a pilot is busy in flying, the phrase used it in the air.
In your example, it will appear as:

...she preferred to keep comms chatter to a minimum when she was in the air...

It would be possible to say: AIRBORNE.

Here is one more that might help...
aloft

Another option not yet mentioned, from U.S. military jargon, is in country, though this carries some contextual baggage. It's similar to in enemy territory and might be used by, for example, a carrier pilot while in an assigned combat or patrol area. It might contextually suggest to the reader that radio silence or strict concentration is important to the specific mission at hand. It would be less fitting if you want to suggest to the reader that this pilot's general, personal preference is simply to avoid chit-chat in the cockpit.
There's also the phrase sterile cockpit which just means a policy of avoiding distractions in the cockpit. This is a common phrase among pilots and would be used as in "She preferred to keep a sterile cockpit."
(Of course, these nuances will only matter to readers familiar with the jargon. There's always a balance to be struck between impressing those who know the jargon and alienating those who don't. Everyone understands "... while airborne" and pilots won't look at you funny for saying it.)

Not a complete answer, but adding to the list:  In Naval Aviation we used "feet wet" and "feet dry" to distinguish between the (generally) overland portion of a strike mission, and the enroute over-water portion transiting to and from the aircraft carrier.
if you are writing about space you could use something like "weightless", "zero G", "in the vacuum", "minus atmosphere" or any similar made-up slang.

Expanding on something suggested in a comment by ASE user "Grimm The Opiner", one might say "but she preferred to keep comms chatter to a minimum while she was slippin' the surlies..."
Referencing the well-known poem High Flight by John Gillespie Magee, Jr.

In fact this exact phrase has been used in print before, but I can't recall where; answer would be improved by a citation.

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text:
What is the efficiency of running an electric motor from a gas generator?
If you were to run an electric motor from a gasoline or diesel generator, how big would the generator have to be to run something like the Siemens electric engine? Is this a viable model for replacing a heavy piston engine or is it too inefficient?
The link below says standard portable generators are capable of 6.13 kWh per gallon of gas.
The Siemens only weighs 50kg and delivers a continuous output of 260kw. Does that mean I'd need a generator 42.4 times as powerful than most portable generators and be burning a gallon of gas a minute?
I know a lot of small aircraft engines weigh around 150kg and several use gear boxes as well.
So Does this mean you could save the weight to make the plane electric but not battery powered or is the generator simply going to be too inefficient?
https://www.google.com/amp/s/settysoutham.wordpress.com/2010/05/26/portable-generators-about-half-as-efficient-as-power-plants/amp/

My aircraft burns 9 gallons per hour, in your scenario, you'd be burning 60 gallons per hour, doesn't seem like a win to me.

Valid, but could a larger generator make it more efficient, especially if it were closer if it's closer to a Beechcraft bonanza than a Cessna 172?

The conversion isn't free, so why not just hook a propeller to it and cut out the middle-man? The issue with the larger generator is that you also have a larger stator, meaning more (very heavy) weight. Even if it was 100% efficient you are reducing the useful load and space. A small generator can extend the range of batteries, but really isn't going to replace them. I know somebody here has the math.

Guess I was thinking about the weight savings wrong. I figured the energy conversion would lose power but wondered if the weight made up for it. Sounds like not. If there were alternate forms of power generation then maybe?

Are you asking if it is more efficient to use chemical energy from petrol/diesel and convert it into electrical energy, than to use the chemical energy directly as in a petrol engine?

No, because you'll always lose in a conversion. Just curious if there could be enough of a weight gain somehow to make it worth it

Which weight saving were you referring to? You need a generator don't you? Either that or an extension cord.

But it doesn't need to handle be torque of the prop and can this be smaller/less heavy, right?

No not really. A generator that can generate 100 kW contains a pretty similar engine to an aircraft engine generating 100 kW of power. The aircraft engine driving the prop directly saves the weight of the electric engine.

Sounds like I've got my answer then

A scenario like this would work in cars, due to weight being a less important factor, and due to the car accelerating and stopping often and the electrical circuit is able to store the power from deceleration of the car and reuse it for acceleration. In city traffic that is. Airplane engines work at a constant load that is much higher than the load on a car engine on the freeway, and there is no deceleration energy to be reused.

Submarines and big boats usually convert motion to electricity to motion.

There are some experimental airplanes flying with a hybrid system like that. E.g. the e-Genius (http://www.ifb.uni-stuttgart.de/egenius/) has a small Wankel diesel engine for range extension (>300km on batteries, 1000km with the wankel). The results are propably good- in the next version they will be using a larger diesel engine.

The big advantage of electric engines in locomotion (and cars) is that in most engines you can get max torque at a stall speed, just starting the motor.  So no transmission is needed.  Airplanes have a rather uniform torque, especially if fitted with a variable pitch prop, which these days means a constant speed prop.  So no transmission is needed. Since the engines can be mounted close to the prop, there is no need to relocate the powerplant. So in short, there are no real reasons to have an electric drive motor for an aircraft.

I know a lot of small aircraft engines weigh around 150kg and several
  use gear boxes as well.

Almost no piston aircraft use gearboxes. The only one that I know of that ever did was the Porsche Powered Mooney PFM which was largely a failure overall, with the gearbox being often cited as an issue. Smaller turbo-prop planes do use gearboxes due to the super high RPM range of a turbine but those are generally larger than the ones that seem to be in question here.

So Does this mean you could save the weight to make the plane electric
  but not battery powered or is the generator simply going to be too
  inefficient?

As mentioned the issue here is simply weight and line loss. You are taking mechanical energy converting it to electrical, bussing it somewhere then converting it back to mechanical. There will always be line loss in a process like that when you don't really need it (since you need to spin the prop to begin with). Gas-Electric (be it diesel or gasoline) is advantageous as you can drive full torque at 0-RPM which is useful when getting a giant freight train rolling but does not provide a ton of benefit to light aircraft. You are also introducing at least 3 major points of failure (engine -> generator -> motor) to a system that previously only had one.

The compare/contrast with diesel-electric locomotives is especially instructive... such systems do very well in that field meeting their needs & working within their constraints, where volume is large and weight is actually considered a good thing. The completely different needs & constraints in aviation drive entirely different solutions. Jet propulsion is great, but not for locomotives!

Analogous to train powertrains :). The great characteristic of electric motors is the large torque generation at standstill, compared to combustion engines. We all tend to look at power output for engine comparison, but it is Newton's second law that provides the acceleration to achieve the end velocity: force (or torque) does that. Power equations just make the computations easier, especially if torque is a function of rpm and if there are gearboxes with selectable gears.
The four stroke petrol (gasoline) engines provide zero torque at standstill and a pesky amount of torque at idle. Two-stroke engines, diesel pistons, gas turbines, electric motors all provide more torque at standstill or idle. Ships have 2-stroke diesels for all the torque that the propellor must provide. Trains indeed use the combustion engine-torque motor combination for better torque control for heavy trains, the alternative is a slipping clutch which has obvious drawbacks. Cars now have combustion - torque combination with batteries to regenerate energy that would otherwise be lost from deceleration.
So if we treat your question as a design question, we can see the reasons why electric motors were successfully applied in other vehicles: to overcome a dominant design issue. In aircraft there are three dominant design issues: weight, weight and weight. And safety. An aircraft that is too heavy simply will not fly. Sure a B747 freighter can lift a tank, but the skin is made from aluminium, the engines are twin axle gas turbines (high torque, low weight!), and everything in the aircraft has been designed for low weight first.
Aircraft don't need slip clutches, the air itself does that already. They just need a light way to create a lot of torque and output power. They also need redundancy: if you have one gas turbine providing electricity for four motors, and the turbine fails, all four motors stop. If you have 4 separate gas turbines, failure of one of them is not catastrophic. For preventing failures aircraft need simplicity. Converting kinetic energy to electrical to aerodynamic propulsion is too complicated.
All of this will be a different story once we can generate electricity in huge amounts from light weight fuel cells, but we haven't cracked that nut yet.

What you describe sounds like a gas-electric transmission (gas/diesel engine drives generator, generator drives one or multiple electric engines that propel the device).
Such systems are sufficiently efficient and very common in trains, ships and other big, heavy and powerful machinery.
Seems that nobody ever attempted to build a plane like that, but, to my opinion, it should fly. There may not be enough benefits to justify the additional weight of the generator and powerful electric engine. For instance the possibility to place the larger and heavier gas engines anywhere in the plane and distribute their power evenly between all (multiple) propellers may be an advantage.

Nobody attempted that indeed, and that may tell you something. What they did successfully attempt is to transfer high required power via hydraulics. Hydraulics! The leaky noisy stepdaughter of power generation, and the aeroplane version uses oil that does not burn but will happily dissolve your arm if given a chance. Simply because of the weight. Unfortunately, weight may prevent aircraft from flying.

@Koyovis Nobody attempted that: In the last aeronautic trade fair I visited there were at least four companies offering such systems. In the past there were no lightweight electric motors, but nowadays experimental airplanes using a gas generator and electric motor(s) do exist.

@Gypaets Well that is good news, and it means that in 20 years time there may be very mature aeroplanes flying around in that configuration. What advantages were their sales teams promoting?

@Koyovis I didn't speak with the sales team, but it is difficult to power multirotor/distributed propulsion systems like the Volocopter with a piston engine attached to each propeller. In the e-Genius case the propeller is placed in a really efficient place were only a small lightweight motor fits (try attaching a piston engine to the top of your vertical stabilizer). The same 2m diameter propeller at the front connected directly to a piston engine would require a much heavier landing gear. It probably pays off.

I understand. Was just curious how the Volocopter would compare to a similar platform with one big propellor.


text:
Why is it not practical for the USN T-45 to be fitted with oxygen systems used in other trainers?
Back in April, the US Navy (USN) grounded all of its T-45 training flights due to issues with the cockpit oxygen system.  I personally heard about this before the grounding secondhand from someone in the program, who was familiar with an instructor who did not remember landing during a training flight.
A number of questions arise, but in order to keep with the single question style that seems to be preferred on this board, I will limit myself to one:
Why is it not practical for USN T-45 trainers to be fitted with oxygen systems used in other trainers?
The T-6 Texan II, used in the USN Primary Pilot training phase uses an onboard oxygen-generating system (OBOGS). I would assume that the US Air Force jet trainer uses one as well.  It surprises me that with a problem that has spanned several years and with a program that has been grounded for three months (and counting) and no solution on the horizon, such alternatives are not being considered.

My guess (with over 2k hours in mil jets) is cost. Despite being what is easily argued "safety of flight", this is not merely "buy one O2 system for each jet"; on top of the safe-for-flight testing, it would likely require structural changes due to where pipes/hoses/cables are placed. The T-45 specifically has very little room for any type of growth.

(For the record, I'm not saying that's a good reason.)

Fitting an entirely different oxygen system is like using a sledgehammer to crack a nut. They need to find out what's wrong with the existing system and roll out a fix. It could be something as simple as a seal, it just takes time to resolve these kinds of issues.

Remember as well that the Goshawk is a modified Bae Hawk, a British design from the 1980s rather than an American design. I'd not be surprised if the entire electrical as well as mechanical hookup is different from that used by US manufacturers

@Pondlife, I guess I'll really know I've made it when you don't find a valid reason to edit one of my posts ;-)

Given that this system is mature, and that  the T-45 has been used in Navy Jet Training since about 1989, and that OBOGS systems are in use in multiple TMS in Naval Aviation, your question misses the point.  The question is, with a mature system that has worked for over two decades, what has changed?  That is what requires investigation and some internal honesty.  (While I have some suspicions, they will remain private until I know more). As with most systems and maintenance issues, fix the problem, which means find the root cause.  (As a reference, see UH-60 Spindles two decades ago).

For another reference point, see the stall fences on the top of an F-18's wing.

@KorvinStarmast agreed, thus my mention of having a number of questions.  I'm certainly interested as well in why this started now on a mature platform.

I guess my other concern is - how do you not it's not practical to put in a new system used in other trainers? (I certainly don't)  The question presumes that it isn't practical; nobody can answer that until what the root cause of OBOGS current failings is known, and then find out what it costs to remedy that versus ... doing something else.  Cut and past of an oxygen system from one TMS to another is hardly the way systems integration works anymore.

@KorvinStarmast fair enough.  I guess what I'm really asking is "Why aren't they doing that?".  I'm giving the USN (or the private contractor responsible) the benefit of the doubt for having considered and ruled out this approach.  If the consensus is that I've assumed too much, I'm happy to change my question.

A new OBOGS wouldn't necessarily help. The Hornets, Growlers, F-15s, SR-71s, U-2s, F-22s, and (recently) the F-35As (of various batches, but not B and C models) at Luke (but not elsewhere(?) strangely) and Super Hornets all have had previous hypoxia-like events, despite using some very different O2 systems over decades. In a recent T-45 event, even pure O2 did not help. Hypoxia root causes can be tricky to track down, some not related to OBOGS.

I think that since this is a current thing that even those in it have not successfully answered to their own satisfaction, I suspect that this question, as of this date time group, may be unanswerable ... until some time in the (hopefully near) future. But It's A Good Question in the sense of "what's the fix?"  or "why this fix?"

:-) I'm glad to hear you're happy with the reasons!


text:
How is wind measured at this small U.S. airport?
While launching gliders at Front Royal, VA (KFRR) over the weekend, a fellow pilot and I got curious about the airport's weather equipment.  We know that KFRR has local equipment to measure wind speed and direction. There is a screen in the FBO that shows a graphical readout of the wind situation.  However, it was not obvious looking at the equipment itself how this is done.
Here are two pictures I took:

Nothing on either of these two pieces of equipment was actively spinning or being visibly affected by the wind.  At the time we has a 10-12 knot headwind almost directly down the runway.  This equipment is ~40 feet to the left of the runway threshold.
Question: Is one of the pieces of equipment I've photographed responsible for measuring wind speed? If so, how?

Hey, would you mind adding your imagery to http://weather.gladstonefamily.net/site/KFRR, as it looks to be a public resource for ASOS station imagery?

@JeopardyTempest Done.  I've also adjusted the marker on the satellite map to one of the two "parts" of the installation.

The device used to measure wind speed is called an anemometer. The one that spins with 3 spoon-like arms is just one type. There are some that have a propeller or fan that spins like a windmill. There are other types that aren't so obvious, such as the ultrasonic anemometer that has no moving parts, but instead uses ultrasonic sound waves to measure wind velocity, it was developed in the 1950s. (https://en.wikipedia.org/wiki/Anemometer)
Actually, if you zoom in on your second photograph you can see the ultrasonic anemometer immediately above the lights on the tower, and below the very top of the tower. It looks like three vertical fingers pointing up.

Also, since you are a pilot, you are already familiar with another type of anemometer that doesn't have moving parts, a pitot tube is a type of anemometer. So long as the pitot tube weathervanes into the wind, it can be used to measure wind speed as well.

Ultrasonic anemometers are replacing the traditional cup anemometers in automated weather stations.  The sensor measures the time it takes for an ultrasonic pulse to travel between the probes, which is affected by wind speed. In your second image, the object directly above the lights appears to be an anemometer.

Source
Ultrasonic sensors have the advantage of no moving parts and lower maintenance requirements. Also, with additional probes, they can measure the wind in 3D.

Thanks fooot and @Devil07 for your answers, both the same and both correct (I assume from the votes).  Very helpful!
I'm not sure what the protocol is when two answers are correct, since I can only check one of them.  Veterans please advise!

@bclarkreston -- pick whichever answer you found more helpful :)

Here is direct information on ASOS stations showing that ball and cup anemometers have been the standard, but can be replaced by sonic anemometers in locations that have freezing issues.  No idea if there is a newer push to further move towards sonic anemometers network-wide.

Thanks @JeopardyTempest...yours is arguably the most detailed response, as the linked PDF very thoroughly explains each piece of equipment used in an ASOS station.

Like the ultrasonic type, Hot-wire anemometers have no moving parts - they measure airflow / wind speed based on how much heat is dissipated from a wire, although these are rarely used for atmospheric measurements.

@kabZX The main advantage of hot wire anemometers is to measure high frequency changes in velocity (e.g. inside turbulent flow). For airfield "wind speed" meteorology, there is no advantage in using a fragile instrument that can measure something irrelevant for the application.


text:
How do instructors simulate instrument failure in basic training aircraft with glass cockpits?
While working towards my private pilot's license in the United States in 2004-2005 (in a steam gauge only airplane), I very much remember my instructor covering one or more instruments to simulate failure and recovery techniques.  He used covers which are commonly available in pilot shops:

I don't remember the examiner asking me fly under such conditions, but this type of failure is covered in the FAA PTS both for private and commercial.
Now that more and more pilots are training with glass cockpits, I was wondering how covering instruments the same way would work.  For reference, let's take the Garmin 1000, standard in the Cessna 172 Skyhawk, which I have to guess is one of the most common civil aviation trainers:

I am, of course, assuming it would be much more difficult to cover the altitude indicator, airspeed indicator, artificial horizon, etc. on a glass cockpit display, not to mention being a questionable practice on a multi-thousand dollar LCD screen.
Then it occurred to me that perhaps the glass cockpit manufacturer would just provide the ability to temporarily disable specific instruments.  But (at least for the G1000) I did not find this feature in the manual.
To summarize, my question is, how do flight instructors/examiners simulate the loss of one of the "six pack" flight instruments in an airplane with a glass cockpit?

You can use a post-it note and you can cut it to whatever size you want and put it directly on the glass.

Perhaps the avionics system has training mode which allows for the disabling and hiding of certain displays? It is software, I am rather surprised that's not a feature at least in more fancy systems

For conventional instrument gauges, I recommend the disks above for blanking out the attitude indicator or the DG/HSI.  Post-It notes are also a common way to blank out instruments to be used.
For partial panel work in glass cockpits, manufacturers and pilot supply shops sell soft stickers custom made for this purpose.

Why don't the glass cockpit manufacturers include a feature to disable instruments for training?

Based on the bounty description, the bounty poster would like to see how a failure of the Attitude and Heading Reference System (AHRS) would be depicted. Unfortunately, that would be the hardest partial panel instrument failure to simulate. There are no stickers that I have seen that will cover the entire Primary Flight Display (PFD) screen while leaving the Airspeed Indicator (ASI), Altimeter, and Heading Indicator (DG) visible. Although, one may be available for purchase.
Conversely, my instructor would just dim the PFD down to near 0%. Then, I would have to fly using the backup analog instruments and the magnetic compass. Also, some PFDs like the Dynon Skyview models have the option to switch the displays to instead represent an analog six-pack. This would make covering each individual instrument easier.
All aircraft certificated to fly in IMC with a glass panel have to have a separate set of backup avionics. These are either analog or glass. They have to have an independent power source like a backup battery or vacuum system. The purpose is to get the aircraft safely to the ground as soon as practicable after the main avionics fail.

Lots of good answers to this question; I especially liked the note about the option to switch to a traditional 6-pack style style display.  Interested in trying to understand how well pilots trained in glass cockpits would be prepared to deal with fail of attitude indicator, and/ or full failure of vacuum system, if they were to fly an older aircraft with traditional "steam gauges"...

@quietflyer - Studies have shown that a glass panel pilot may not necessarily have trouble using analog instruments. But, they usually have a lag time in switching from the glass panel to the analog backups during a systems outage. The transition time to the backups is much quicker when the backup is also another glass panel like the Aspen Evolution. Flying partial panel without an AI at all is made easier if there if the backups include a Turn Coordinator. This is typical in aircraft with G500s (like the Archer III). But, it is not typical with G1000s (like the C172SP or the Archer TX).

In my case, my primary training for PPL was all in glass panel aircraft. All of my instrument training was done with the glass panel turned off, relying on the steam gauge backups. Some of that was done with the backup Attitude Indicator covered to simulate partial panel. A G430 was used for VOR indications. And, most of my rental time and my simulator time has been in steam gauge aircraft. The biggest difficulty is not in the difference in appearance since backups look like any other steam. It is in trying to ignore the steam gauge AI when it goes bad. A big red “X” does not cover the gauge.

@quietflyer - So far, I have had 3 or 4 actual steam gauge AI failures in rental aircraft without any incident. Most were in the same aircraft. What was challenging in renting older aircraft was trying to fly simulated IFR with an OBS when I had spent all of my previous experience with an HSI

I believe that behind the panel, the wires connecting the G1000 to the 3 or so computer boxes can be removed one-by-one, rendering each instrument on the glass face inoperative. - However, this should never be done without a technician.
Another option is to black out or cover the screen entirely. This one I've seen done before by pulling the circuit breaker to the monitor for an example on the ground, not in flight. Do note that this kills the display entirely, and is not recommended to be done without a technician, if at all.
As required by Transport Canada or C- registered aircraft, the aeroplane must be equipped with a traditional ASI, ALT, and HI underneath or to the side of the G1000 in case of an electrical failure, as well as a traditional magnetic compass that is usually mounted on the dash. If that is followed, the previous might be able to be done. However I've never attempted it, and I probably never will - Again something that should be approved by a mechanic/technician.
Under normal training, I've never had the attitude or heading indicators blocked out on the G1000. Sticky notes are used to block out instruments on the second 172 that does not have a G1000 at my local flight school.
As a last (and most realistic) option, refer to pages 6 and 8 of this manual on the FAA site:
https://www.faa.gov/training_testing/training/fits/guidance/media/g1000.pdf
Hope that answers your query

Welcome to AviationStackExchange.

Unless you are an A&P aviation maintenance technician, I would strongly advise against disconnecting any wires from your glass panel. I would also advise against constantly pulling your circuit breakers to the AHRS as recommended in your link. This is an especially bad idea in flight since the AHRS will have to re-selfcalibrate at a possible non-stable attitude when brought back online. Especially since it is much easier to just dim the screen to make it unavailable to the student pilot. If CAA regs are similar to the FAA’s, not every glass panel aircraft requires backup instruments.

Search the term “standby” in the following FAA Advisory Circular, AC 23.1311-1C - Installation of Electronic Display in Part 23 Airplanes. This allows for multiple PFDs or displays with reversionary mode to be used as primary flight information instead of traditional analog backup instruments.  https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_23_1311-1C.pdf

@DeanF. I'm not 100% familiar with the FAA's glass cockpit regs, but as far as TC goes, the four instruments I listed in the original answer.
You are indeed correct about removing wires and will update the answer accordingly

By TC, I assume you mean type certification. As an example, an aircraft can be certified for VFR flight only. In which case, they would not need to have backup analog gauges. Especially if the PFD and MFD had a reversionary mode. Light Sport Aircraft like the Czech Sports Cruiser are an example of this. Aircraft certificated for IFR can replace all of their analog backup instruments with one independent backup PFD like the Aspen Evolution backup display. It is a self-contained glass panel with its own ADC, AHRS, and battery power source.

No, by TC I mean Transport Canada.  Our equivalent to a type certification is a type rating, or TR.

And, curiously, an FAA type rating is what goes on a pilot’s certificate that authorizes him or her to fly a specific model of aircraft within the Category and Class of aircraft in which they are certificated. To fly a Piper Aerostar, you would need an Aircraft, Multi-Engine Land certificate with a high performance and a complex endorsement. To fly a Embraer Phenom 100, you would need an Aircraft, Multi-Engine Land certificate with a Phenom 100 type rating.

Manipulating panel instrument controls for partial panel training can be accomplished in a static flight simulator training environment in professional flight schools. T
Pulling circuit breakers is unwise in any live training scenario, on the ground or in the air. Putting a post-it note over a panel was the recommended path used by my instructors in the live environment in military or civilian training.


text:
Mathematically calculate Mach number using CAS and PA WITHOUT flight computer
I am just wondering how to calculate the Mach number from CAS and Pressure Altitude WITHOUT the use of a flight calculator.
E.g Given FL300 (30000ft) and 325kt CAS find and Mach number.
I have always used an old-school flight computer but now I am just curious about what's the math formulas behind it.

And… a handy close approximation for calculating P from baro altitude, H (in ft) is: for H = SL to 36,089 ft:  P = P_SL(1 - 6.87535E-6H)^5.265 and for H = 36,089 to 65,617 ft:  P = P_SL0.22336e^(-4.80634E-5(H - 36,089))*

You can use the following formulas for conversions (source: aerotoolbox.com):
$$ M = \sqrt{5 \left[ \left( \frac{q_c}{P} + 1 \right)^{2/7} - 1 \right]} $$
$$ \text{CAS} = a_0 \sqrt{5 \left[ \left( \frac{q_c}{P_0} + 1 \right)^{2/7} - 1 \right]} $$
with $q_c$ as impact pressure, $ a_0 \approx 340.3 \, \text{m/s} $ as sea level speed of sound and $P_0 \approx 101 \, 325 \, \text{Pa} $ as sea level pressure.
Solving the second equation for $q_c$ gives:
$$ q_c = P_0 \left( \left[ \frac{1}{5} \left( \frac{\text{CAS}}{a_0} \right)^2 + 1 \right]^{7/2} - 1 \right) $$
Plugging your example $\text{CAS} = 325 \, \text{kt} \approx 167.2 \, \text{m/s} $ in gives:
$$ q_c \approx 18 \, 181 \, \text{Pa} $$
At FL300 we have $ P \approx 30 \, 090 \, \text{Pa} $. With the calculated $q_c$ we can now calculate the Mach number with the first equation above:
$$ M \approx 0.8502 $$

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
Can anyone identify this photograph - what aircraft, when and where?
This is a large photograph, with nothing on the reverse, so any help would be welcome.

Many thanks for your time in helping to identifyt this aircraft - much appreciated.

The twin-mast configuration is typical of the Deperdussin Monoplane, possibly known as the Deperdussin 1910 Monoplane, or the Deperdussin Type B monoplane, which first flew in 1910.

Source: Wikipedia
This example in the Musee de l'Air in Paris has a different fuel tank and cowling configuration.

Source: Flugzeuginfo.nat
The exact nomenclature is not clear from what I found. Many sources referred to this as the Type B monoplane, but it seems that although Deperdussin produced a catalogue that included Type A to Type E, they didn't commonly use those names at the time.
The aircraft is recorded as competing in a number of events around Europe and the US, so I can't place the location of the photo, nor date it more than 1910 or later.
There remains one airworthy example at the Shuttleworth Collection in the UK which I remember seeing being flown sometime in the late seventies. It takes a more intrepid pilot than I to climb aboard those early aircraft!

"more intrepid" -- surely, not least because control layouts weren't standardized until at least the onset of the Great War.  Some of the early airplanes had Zeppelin style controls (one wheel for right-left, another for up-down).  Rudder pedals weren't universal, etc.

It is a type of Deperdussin monoplane which was first flown in October 1910.
Many were built, and several have survived, including an airworthy example in the Shuttleworth Collection in England.
Most were flown in Europe, but two were used at the Central Flying School at Point Cook, near Melbourne Australia.


text:
Why air pressure is raised twice in air cycle machines?
Currently studying about aircraft air cycle machines for my midterm, and this question still kinda stuck in me.
So in air cycle machine, in my understanding, the air pressure is raised twice. But I still don't understand, why is that?

You have a system that takes hot high pressure air that was compressed in the engine, removes the heat while it is still at high pressure, then lets the pressure drop, reducing its temperature to below its starting temperature.
But the potential temperature drop is not sufficient if all you do is remove the heat from the initial bleed supply using nothing but heat exchangers, then let it expand to get your chilling effect.
But what you CAN do is exploit the kinetic energy in the flow, to repeat the compression heating/heat-removal-while-compressed cycle a second time and get a much larger final temperature drop. This is what the Air Cycle Machine does.
You use the velocity in the air flow to drive a turbine that drives a secondary compressor. Kinetic energy in the flow is extracted and converted into heat by raising the pressure a second time, then extracting the extra heat created by the secondary compression, through secondary heat exchangers.
So air coming from the engine was hot at high pressure, some of the heat was removed in the precooler, without reducing pressure and velocity, then the velocity energy is extracted to raise the pressure and temperature of the partly cooled air more, its excess heat is removed with secondary heat exchangers, then when the air gets to the other side of the turbine, it's allowed to expand to a much higher volume having both its heat and kinetic energy extracted, and the temperature drop is more extreme.
The double cycle - compression/heat removal/compression again/heat removal again/expansion to ambient - can take air leaving the compressor at, say 300 deg F, and chill it down to -40F. You can't allow that to happen because ice will form on the turbine, so you have to limit the discharge to just above freezing with the control system, but that's how efficient a "bootstrap" compressor ACM is.

Inside the air cycle machine, air pressure is not raised twice.  However, the machine is partly powered by high-pressure "bleed" air, so in a larger context the pressure has been raised before it enters the air cycle machine.
The air cycle machine (pack) cools the bleed air, compresses it, cools it again, then runs it through a turbine, a hot/cold mixing valve, and usually many other sensors and components that make the system very complex.  By the time this "twice compressed" air reaches the cabin at sea level pressure, it can be extremely cold.


text:
What is the difference between a 1974 Cessna 172 and a Cessna 172M?
Are there any discernible exterior features that are different for a Cessna 172 vs 172M?
If a Cessna 172 was made in 1974, is it an "M" series?

Does this Wikipedia page answer the question?

Welcome to aviation.SE! As a general suggestion, if you want as much detail as possible on the differences between specific models then the definitive reference is the Type Certificate Data Sheet. Although it might not help much with exterior features, considering that factory options, avionics upgrades, STCs and so on can all change an aircraft's appearance.

Yes any 1974 172 is an M.  Cessna changed the letter designation with each significant design change. Through the 60s and early 70s, this was annually, so each year relates to a letter.  The M however was a configuration that lasted 4 years, '73 to '76.
The follow-on N was also built for several years in the late 70s, but suffered from the H2AD engine fiasco.  The M being 4 years of production, and coinciding with the big GA boom of the mid to late 70s, it's probably the most plentiful of the older 172s and is considered by some to be the best used version to purchase from a features vs price perspective, having most of the major improvements in the basic design (cuffed leading edges, tubular gear, etc.).  An N is also in that category if it's had its engine replaced by a different Lycoming model.


text:
On the Airbus A320 family, when does the autothrust disconnect?
I know you can press the AT disconnect button on the sides of the throttle.
You can press the A/THR button on the FCU.
When does it disconnect automatically? For example, on landing.

The autothrust disconnect is described in the Flight Crew Operating Manual:

A/THR DISCONNECT
When the A/THR is disconnected, it is neither armed nor active.
The A/THR can be disconnected in two ways:

Standard disconnection

The pilot pushes the instinctive disconnect pushbutton on the thrust levers (which immediately sets the thrust corresponding to the lever positions) or
The pilot sets both thrust lever to IDLE detent.

Non-standard disconnection

The pilot pushes the A/THR pushbutton on the FCU while A/THR is armed/active, or
The system loses one of the arming conditions.

(Airbus A320 FCOM - Autoflight - Flight Guidance)
On landing, the autothrust is actually not automatically disconnected. The Airbus will remind the pilots to retard the thrust levers to idle with the "RETARD, RETARD" callout when passing 20 ft (see e.g. this answer). Moving the thrust levers to IDLE will then disconnect the autothrust system.

Bringing the throttle back to idle on landing and A/THR disconnecting - is there an RA requirement for that to happen or will that happen at altitude also.

@dashman You start to smoothly retard the thrust levers at the "RETARD, RETARD" callout (20 ft RA) and ideally they should reach the IDLE detent in the moment of touchdown.

I don't think I was clear. If I bring the thrust levers back to idle at 1000 AGL - will the A/THR disconnect or only below a certain RA.

@dashman Ah, sorry. Yes, the A/THR will always disconnect when both thrust levers are in IDLE, regardless of altitude.

This somehow links with TAM accident mentioned in  this question, and you also answered. I guess the spoilers didn't deploy because the A/T was still active.

Reading the TAM report, it seems even if you bring 1 thrust lever to idle, A/THR is disconnected.


text:
How to calculate the lift coefficient of a multi element airfoil?
How to calculate the lift coefficient of an airfoil section with flaps and slats if we know the Cl for the individual elements, like Cl of wing, Cl of slat and Cl of flap?

It depends. Are the c$_l$ values referenced to the local chord? Then you need to convert them to the chord of the full airfoil so they can be added.
I wonder, however, how you can have individual lift coefficients without the total lift coefficient. If the single parts are isolated, their pressure distribution is different from that in the context of the full airfoil. Please check the source of the lift coefficients and make sure that they are representative of the local lift when flown in combination with all other parts.
Normally, what needs to be done is to use a multi-element airfoil code and calculate the lift coefficient of the full wing with all high-lift devices in place.

The number one error by students doing piecewise analysis is to ignore the multi-chordal relationships.  In other words, the chord of the wing, vs the chord of the flaps and of the slats. Normally the reference is the fixed portion of the wing chord.

@mongo: No, the reference should be the chord of the full wing with all devices retracted. But in the end a common reference is what matters most. Even if you use the length of the untied shoelace of the wind tunnel technician.


text:
Is there a formula to calculate how big a ventral fin should be?
I've been doing some research into vertical stabilizer designs for a university assignment and have come across ventral fins. I've found a fair bit of information on why they're fitted but can't find any formula or rules of thumb to determine how big a ventral fin should be.
I was wondering if anyone knows any of the maths behind ventral fin sizing and the stability it provides?

There is no single formula - the number of factors to consider are too numerous and the load cases are too diverse. Here is an incomplete list:

Directional stability: Depending on fuselage size and shape, the tail must be sized to pull the aircraft into the wind direction. The fuselage is destabilising in yaw and the tail is needed to counteract that. Depending on factors like wing sweep, some of that stabilisation can be contributed by other parts of the airframe.
In multi-engined aircraft: Yaw from asymmetric thrust. If one engine fails, the fin must be large enough to create an equal but opposite yawing moment to that of the still running engine on the other side. Multi-engined aircraft have a minimum speed below which directional control with one engine inoperative is lost.
In high aspect ratio designs: Counteract adverse yaw. When ailerons are deflected and the aircraft rolls, the direction of lift on the side with the trailing-edge-up aileron tilts forward and vice versa. This horizontal lift component creates an undesired yawing moment that the tail needs to neutralize. This effect varies with speed, so if you want good low-speed maneuverability, this load case determines vertical tail size (mostly of gliders).
Dutch roll damping: Sometimes static stability in yaw is not sufficient and dynamic stability sizes the tail.
Maximum flight Mach number: At high Mach, the upper side of the plane flies in less dense air and a traditional vertical tail loses much of its efficiency. Here a ventral tailfin can help to reduce tail size considerably.

Add to this the fact that the destabilizing effect of the fuselage increases with sideslip angle and the fact that the vertical tail as the higher aspect ratio surface of the two will reach its maximum lift first and suffer a noticeable decrease in effectiveness at larger sideslip angles. Now details like a highly swept fillet are needed to maintain tail effectiveness at high sideslip angles.
Finally, it depends which of the load cases is sizing your tail, and that can be determined by factors like fuselage length. Tail effectiveness for directional control grows linearly with fuselage length and for yaw damping with the square of fuselage length. If you want to fly the same tail on fuselages of different length (like most airliner models do), your tail might be sized by a different load case on a different aircraft than the one it is mounted on.
If you want to fly low and fast, it might be that the loads on the vertical deform the structure so much that the efficiency of the vertical tail is greatly reduced. In that case it does not help to make the tail bigger, instead ventral fins must be added. Now you need not only to look at the best tail size but at the best overall tail configuration as well.

With subsonic airliners ventral fins are usually a stopgap, put in place because flight tests have shown that the vertical tail as designed and built, lacks effectivity for stabilising. It is much easier to add a ventral fin than to extend the vertical tail: the tail root will need to be re-designed to accommodate the extra bending moment. Or they are added to compensate for the de-stabilising effect of a modification, as in this Gulfstream:

Design and dimensioning of the vertical tail of an airliner is not straightforward, due to the many interference effects from the fuselage and the fuselage-wing intersection. From Torenbeek section 9.6:

The design of the vertical tailplane is more complicated than that of the horizontal tailplane. It is generally quite difficult to calculate the lateral-directional aerodynamic characteristics, since they are closely connected with a complicated asymmetrical flow field behind the wing/fuselage combination, which meets the oncoming air at an angle of sideslip.

The book gives a design process for determining the tail volume (tail area * moment arm). There is a relatively large number of input variables:

number of engines;
location of engines;
high/low wing;
vertical position of horizontal stabilisers.

Figure 9-24 above from the same book is for rapid dimensioning of vertical tail volume of single engines or wing root mounted engines, Figure 9-23 is for multi-engined aircraft. There is no design procedure for sizing ventral fins in the book, but they would follow the same design principles regarding vertical tail volume.
With airliner size aircraft, a big part of the solution is numerical computation. The engineering simulator will have a detailed 6-DoF model of the aeroplane, including aeroelastic effects and the flow field behind the wing/fuselage intersection. Ventral fin dimensions and placement can then be test flown on the engineering sim first.

...unless it's a 707, where the ventral fin was added as a bumper to protect the airplane in the event of a tailstrike.


text:
Is "Pull up and be ready" standard phraseology?
I was next in line (making IFR departure) just after a Bonanza departed, with about a dozen aircraft behind me. Tower called my number and said "pull up and be ready".  I'm accustomed to "line up and wait", changed from the old "position and hold", so I was expecting "line up and wait".  We're always taught to get clarification if we don't understand, but the tower guy seemed disgusted with me for asking, as if "pull up and be ready" is "duh"... standard phraseology.  I've never heard it before, or since, so am I needing to study the AIM a little bit more?

It isn't standard phraseology, and a controller should never use the words "pull up" when directing traffic unless they are trying to avoid a collision. I don't think you were in the wrong here.

Probably that guy doesn't know standard phraseology. A Google search of pull up only brings up an exercise adults do or a training toddlers do.

Imagine pull up your pants and ready....

You might consider submitting a NASA ASRS report on this (I assume from your mention of the AIM that this happened in the US). Not necessarily for your own protection - asking for clarification was the right thing to do, IMO - but because it seems like egregiously poor phraseology on the controller's part. I'd listen to the recording on liveatc.net first,
if it's available, just to make sure that you really heard what you think you did.

@Farhan it's also something that automatic cockpit warnings say, isn't it? Or used to say at least.

@AakashM: Yes, it is.

After the fact, I can guess that he meant, "Pull up to the runway hold short line, staying on the taxiway, and be ready for immediate takeoff when cleared".
But his phrasing was non-standard, and definitely confusing.
I think the proper way to say it would have been, "N12345: Hold Short; You are #1 for departure; be prepared to go without delay."
The key parts being:

"Hold Short" is an unambiguous instruction
Informing you that you are next in line.
Informing you what is expected, using the official term "without delay"

Even that is slightly risky, as the "without delay" could be misinterpreted if the pilot misses the initial "hold short" instruction.
I think the proper responses available to the pilot are one of:

"Holding short.  Ready to go without delay"
"Unable"  (I'm not ready yet, perhaps in part because I don't understand)
"Please Clarify" (You used confusing terms; Spell it out for me like I'm 5)

What is not standard phraseology but is somewhat common is an instruction to "pull up to the hold bars and hold short runway 11, be ready to go" -- sometimes followed up with "... I'm going to get you out after the 737 on 2 mile final". That happens in a situation where you may have more than 1 aircraft waiting, none right at the hold bars, without a clear picture of "who's next". The Tower controller is telling the aircraft that IS next, to pull up to the hold line, be ready, because here's my plan. Sounds like the OP got a shortened & less clear version of that instruction.

"You are #1 for takeoff;" should not that be "You are #1 for departure" since this is not a clearance?

@vasin1987: That may be correct, since "takeoff" could be misinterpreted.  That just illustrates the difficulty in picking terms correctly if a controller strays even a little bit from standard phrasing.

Adding my support for the use of "pull up to and hold short rwy xx," which I mainly use if an air carrier has been waiting in the runup area for their wheels-up time. The "and hold short of" is very important.

You’re right, it is neither standard phraseology nor clear what the controller intended (though I agree with others suspecting he wanted you to be ready for a departure without delay).
This is an ideal example of why standard phraseology should be used. Pull up to what? Be ready for what? I could see this easily being mistaken for a LUAW by a less vigilant pilot. You were right to question the controller; good job. As a former tower controller, this makes my skin crawl.
A better choice, among many, would have been something along the lines of, “N123, expect to depart without delay, continue holding short of runway ##.” It is clearer, it does not use words in a standard takeoff clearance (namely “cleared” or “takeoff”), and it emphasizes the need to continue holding short.
I agree that an ASRS report would be useful, if you have the time.

That does not sound like standard phraseology is I’ve never heard the phrase “pull up and be ready“.   If this was a busy airport, the tower may – and I do say may - request an aircraft pull up to the runway hold line and expect an expedited takeoff clearance for traffic separation.   That was a bad job on the part of the tower; the guy should never have said that, as it’s a great way to cause runway incursion.

The busier times at my local Class-C, they usually say "N12345 hold short 24, traffic on short final", or if they are trying to sneak me in: "N12345 cleared 24 no delay, traffic on 2 mile final". Usually I tell them that I'm "holding short" and if I see the traffic they are talking about I'll also say "traffic in sight" so they know I'm looking.


text:
Is the angle of attack equal to zero when the plane is on the ground with wings level?
I read in the internet that when an airplane stands at the airport (horizontal) it has zero degree aoa. The captain must pitch up the plane during cruise to generate an amount of lift and when the airplane pitches the relative wind also changes, and this will affect the angle of attack. This is really confusing me

The angle of attack is not defined when the aircraft is stationary on the ground, since there is (virtually) no relative wind

Yes. No angle to attack.

what about angle of incidence ?

Possible duplicate of What is the reason of having an Angle of Incidence on an airplane?

@Sanchises I don't think this is a duplicate. This is distinctly asking what the AoA is, not why there is an angle of incident. It is however a nicely related question.

@Notts90 I suppose my vote should then go to "Unclear what you're asking" since I really thought the duplicate would answer this question. I thought the question was "Is the angle of incidence generally zero?" to which the answer is "No, see duplicate for why".

To give you some values. For the A320 without wind, the AoA on the ground is usually 0.2°. When the pilot accelerates and the A/C is braked the AoA becomes 0°. During the rotation phase the value goes from 0.2° up to 6 - 8°

You're right to be confused. The AoA can be almost anything, depending on wind direction. Normally, a wing has some camber so the lift it creates in flight is possible with an AoA of 0°. Normally, the wing is mounted at an incidence of a few degrees so the fuselage remains horizontal in flight. With this incidence and horizontal wind, the AoA at rest is just this incidence angle. But if the aircraft experiences tailwind, the AoA can be near 180°. If heated air below the wing rises up as a thermal, the AoA can be momentarily around 90°. In almost all cases, flow speed is much lower than that required for flight, but there are exceptions.

George Guelis says, you do need a positive angle of attack. A flat plate (or a barn door, for that matter), or a symmetrical airfoil, will give zero lift with zero angle of attack

@D.Frederico: Note that I made camber a condition for lift at zero AoA. See here for the difference between cambered and encumbered wings.

you mean a cambered wing can generate lift even with zero degree angle of attack but flat plate or symmetrical airfoil can't

@D.Frederico: Yes.

If an wing is stationary and there is no wind, then there would be no airflow and therefore no angle of attack.  Assuming there was a wind, then there would be a relative airflow and so an angle at which it meets the chord of the wing.
If a stationary glider is pointing into a breeze with one wing on the ground, it is possible to lift the wing off the ground using the ailerons.  This is accomplished by increasing the angle of attack of that wing, creating additional lift, despite the glider not moving forwards.  Conversely, if the airflow was from behind, the ailerons would be used in reverse (opposite aileron) - a consideration for glider pilots trying to keep wings level as they slow down if they land in a tailwind.


text:
What is the purpose of a small wing near the cockpit on the front of some planes?
I saw a plane leaving Luton Airport that I have never seen before.
It seemed to have an extra small rectangular wing near the front of the plane. What is it?

Welcome! You likely saw a canard control surface.

You should provide more details about the aircraft (big or small, prop or jet, etc). Also a picture would be very helpful. Like @mins said, its probably a plane with a canard configuration of some sort.

Since you specified a rectangular canard, could it have been a Piaggio Avanti?

If it was REALLY small, it could have been an Angle of Attack vane.

That would be a canard you see on the airplane.

An aircraft designer may adopt the canard configuration to reduce the main wing loading, to better control the main wing airflow, or to increase the aircraft’s maneuverability, especially at high angles of attack or during a stall
Canard foreplanes, whether used in a canard or three-surface configuration, have important consequences on the aircraft’s longitudinal equilibrium, static and dynamic stability characteristics.
Many pioneers initially followed the Wrights' lead. For example, the Santos-Dumont 14-bis aeroplane of 1906 had no "tail", but a box kite-like set of control surfaces in the front, pivoting on a universal joint on the fuselage's extreme nose, making it capable of incorporating both yaw and pitch control.

I hope this has helped.


text:
Is there an official method to do pre-departure briefings?
We're using our simulator more at university, and while I might try to do a departure briefing (weather, route, etc.), it ends up fairly unstructured. None of us students have any formal qualifications and we are doing this for enjoyment, although we are keen to do it as authentically as possible.
FAA has an example online, that I gather is maybe be a bit overdone:

I've searched around for a recommended (check)list to go through for pre-departure briefings, but come out empty handed.
Is there such a document endorsed by either the EASA or the FAA?

There's no official CRM checklists that I know of, airlines develop their own. These are very structured for a reason, chances are the pilots have never met before, the structure ensures everyone knows what the others will do in the cockpit.

This article on how one company‘s briefing methods were reviewed and improvements suggested may be highly relevant: https://www.aerosociety.com/news/briefing-better/

@CptReynolds this seems to the best material to reference to, would you like to add it as an answer?

The article linked below may be highly relevant, although it isn’t endorsed (directly) by any regulatory body. It describes how one company dissected their briefing concept and proposed improvements following a critical review of the adequacy, effectiveness and safety impact of their briefings in the operational context: Briefing Better


text:
What instruments are used to indicate aircraft attitude in acrobatic airplanes?
As aerobatic airplanes don’t use gyroscopic instruments such as attitude indicators, what instruments are used to indicate the aircraft’s attitude in flight?

One way is talked about here

They aren't doing aerobatics IFR, so the best way to determine attitude is to look out the window, some have additional decides on their wingtips to align the horizon.

The basics:  Acro airplanes don’t have attitude indicators because they don’t need them.  The airplanes are certified at Day/Night VFR flight only and gyroscopic instruments are not required equipment here, not to mention can be precessed and damaged by aerobatic flight.
The only attitude instruments needed here is the horizon itself and the pilot’s Mk I eyeballs to see it.
Sometimes pilots make use of aerobatic sights mounted on the wingtips; these look something like eight spoke cowboy spurs or a 45° right triangle frame and are used to fly certain reference lines during aerobatic flight.
Some acro aircraft do make use of glass cockpits and solid state Attitiude, Heading, and Reference Systems (AHARS) as a safety backup on cross country flights, but they are not used during aerobatic routines.

Aeroobatic aeroplanes might have attitude indicators, or be certified for IFR flight, I think you may be thinking of competition aircraft, however there are a lot of aerobatic capable aircraft that are used just like normal GA aircraft, like the Cessna 150/152 Aerobat, or the American Champion Citabria, Decathlon, and Super Decathlon, mechanical attitude indicators can be equipped with caging mechanisms during acrobatic flight.

I’m aware of very few aerobatic aircraft equipled with attitude indicators or gyro instruments, primarily because the airplanes don’t need them for day/night VFR flight.  An aerobat might but the Citabria/Decathalon line does not use gyro instruments.


text:
What name is given to an abeam waypoint in the FMS?
In a Flight Management System, what name is given to an abeam waypoint in case of DIR TO?
Is this name format different in Thales and Honeywell FMS?

From the Thales Pilot Guide:

If ABEAM PTS are desired:
  ABEAM PTS [3R] .......... Confirm/Press
  If Option 1 is defaulted, ABEAM PTS is displayed yellow, if not press [3R].
ND shows direct track (dashed yellow), as entered, superimposed on existing ACTIVE F-PLN.
Abeam WPTs are named ABxxxxx, xxxxx representing the first five characters of the relative WPTs.
  Ex: ABADAIB, ABBOKNO, ABDEVRO

Honeywell FMS is different:

Abeam Points (ABEAM PTS)
Push -

creates place bearing distance waypoint on the Direct To leg abeam
  the bypassed waypoint if the bypassed waypoint was a database
  airport, navaid, NDB, or waypoint
creates latitude/longitude waypoint on the Direct To leg abeam the
  bypassed waypoint if the bypassed waypoint was a
  latitude/longitude waypoint

So in the Honeywell FMS the abeam points will use the Place Bearing Distance name or the Lat/Lon name depending on the type of original waypoint.

@Federico  Looks good.  Thanks for the edit.


text:
What materials are used for aircraft windshields?
Is hard plastic or some form of plastic replacing glass in aircraft windshields? Any idea/companies/players in this field??
I have heard there is recent trend as plastics are light in weight and have properties comparable to that of glass.

LP Aero Plastics has been making plastic windshields for a very long time.

Somewhere here we have a question about the manufacture of fighter aircraft windshields, though my search-fu isn't up to snuff this morning. It might answer this question, though it might be military specific while this is more general.

@FreeMan ..Thanks!!!  I am covering all three commercial,civil and military aviation.. any leads?

It may have been more on the lines of "how are they made". I remember an answer had a link you a YouTube video showing them making an F16 canopy.

Cee Bailey https://www.ceebaileys.com/Aircraft-Windshields-Aircraft-Windows.html is another aircraft window supplier.  One of the pages mentions 0.25 cast acrylic.

Great Lakes Aero products is another window supplier http://www.glapinc.com/mainmenu.htm  These windows are also acrylic, 3/16" and 1/4" are common for small aircraft.  Recent advances by all companies are adding UV protection and various tinting.

My recent front window came from LP Aero Plastics. 1/4" thick acrylic.

On light aircraft, acrylic windshields have been the norm.  On higher speed aircraft, glass and laminates are used, particularly with heated windshields. The laminates may use polyvinyl butyral (PVB) is tough and ductile which enhances mechanical properties and impedes shattering of glass layers and the transmission of cracks from one layer to another.
Layered products may have various coatings which affect transmission of light and RF, reduce reflectivity, include elements for heating. While I do not know of an aircraft application, it is common in automotive for layers to include radio antennas.
Glass is an amorphous, non-crystalline material and acrylic plastics and glass have very different properties.  Glass tends to shatter with sufficient impact. However, glass tends to have high resistance to temperatures that subsonic aircraft will normally encounter. Glass also retains good clarity properties over the operational domain of subsonic aircraft. Acrylic tends to be pretty shatter resistant, although I know a turkey vulture which proved otherwise (grin). Acrylic is more suspectable to abrasion and scratches, and therefore requires cleaning and maintenance considerations which glass does not.
It really depends upon the type of aircraft and the design criteria, which include the operations, temperature, heat requirements (ie hot windshield for de ice), weight considerations, EMI considerations (coatings, etc.) and so on.
Both materials have been in use for a long time.
So what kind of aircraft are you talking about?

The glass used in airliners is made of several layers, with polyvinyl butyral between them.

@PeterKämpf made an important point, generally glass is laminated to provide better shatter characteristics, and also to permit heated elements, EMI measures, etc.

I have no problem if you add this directly into your answer. Then I can delete my comment.

The focus is on Commercial,civil and military aviation.

"plastic" was used, because to many people that is more readily understandable than a "slow moving, viscous liquid."  We're talking aviation here, as opposed to molecular structure. Physics would be a better group for the discussion of "Colloidal glass transition observed in confinement," which is actually a good paper from Physical Review.

Light aircraft do not use polycarbonate windshields aka "Lexan", they use acrylic-polyvinyl chloride known by the trade name "Plexiglass". Lexan is very hard to polish scratches out (it tends to fray small hairs) and severely yellows with time. Plexiglass can easily have deep scratches polished out and is less apt to yellow from UV. Also, glass is not a type of plastic, it is classified as a liquid (it lacks a crystalline molecular structure).

I'm pretty sure the "glass flows slowly" bit is a debunked myth. See this post on Physics.SE, as well as other articles online (googling "does glass flow" results in a lot of hits that all basically say, "no").

@yshavit, point taken.  I will have to research, and if necessary reach out to my little brother who has a PhD in materials science.  Then I modify my answer accordingly, because I dislike promulgating mistruths.

@yshavit, I reached out to the materials people who have made large mirrors for our instruments.  They laughed. I remember being told in class at MIT about the flow of glass.  Well apparently, aluminium flows more than glass.  Give me a day or so, and I will modify my answer.

@mongo Thanks for the update! :-)

A little late but I see some points the answers above missed and feel the record needs set straight.
Fixed wing military aircraft typically use thick polycarbonate plies laminated with polyurethane inter layer with various EMI coatings.
Military rotorcraft will use much thinner plies of polycarbonate, acrylic or a combination of both with various EMI coatings and extremely scratch resistant outer coatings to protect against all the debris they churn up.
Most commercial and general aviation aircraft have a glass outerply for scratch resistance, heated de-ice/de-fog capability, and static drain laminated to a main ply with polyurethane inter layer. The main ply is typically 2 plies of acrylic laminated with a type of vinyl interlayer. Some aircraft have polycarbonate main plies but acrylic is the norm. Plastic windshields/side panels are much lighter than all-glass windshields but are more difficult to manufacture. For that reason, some commercial/general aviation aircraft today are still designed with all glass windows, but it is a dying trend.
Major players in this field are Sierracin/Sylmar Corp (subsidiary of PPG Industries), GKN, Llamas Plastics, and Texstars


text:
What are some Anti-icing solutions for small planes without an on-board system?
When flying during the winter, is there anything I can do to increase my margin of safety, such as anti-icing fluid?
I've heard of people spraying their aircraft with propylene glycol, but am curious to know if this will do anything to prevent ice after takeoff, especially without a thickener.

Without an onboard anti-icing mechanism, I would say the the best that you could do is to wish that you were in the air.

Generally light GA aircraft have limited anti ice system, usually limited to just pitot heat.  Some newer aircraft have been certified for flight into known icing (FIKI) and make use of chemical deicing methods like TKS “weeping wings” or electrically heated systems like the Kelly ThermaWing.
I will caution you that, even if your aircraft is FIKI certified, this is by no means an encouragement to actively enter or remain in icing conditions.  Rather it is just an additional layer of protection to allow a pilot to escape icing conditions.  GA planes are not transport category machines and do not offer that same level of ice protection that transport catergoy aircraft do.
Also note that these system do have their limits.  Operate outside of them and anti icing systems can be pretty hazardous, as this photo from an acquaintence of mine shows after having used a TKS system in an SR-22 in temps below that recommended for the system.

Even more tragic was this case from New Jersey where a pilot flew a FIKI certified TBM-850 into severe icing conditions and it cost him his life.

Again the systems can help if you get into a pinch and need additional time to escape, but the best course of action is to avoid icing conditions in the first place by doing a proper Preflight, setting personal minimums and strictly adhering to them.........and knowing when to say when.

Is it possible to carry a USB hairdryer to use on the windows and wing edges>?

@Cloud Do you know how much power can be provided via USB, and how much power is needed to melt ice? Hint: the latter is typically somewhat greater than the former.

@aCVn Not much power to melt ice. Even a USB hairdryer can raise the temperature well over zero degrees C.

USB power is measured in Watts, which is Joules per second. Melting ice costs 300 Joules per gram. IOW, that USB hairdryer will melt one gram of ice per 5 minutes. yes, it works, no, it doesn't work on the scale you need it to work.

You could, in theory, use a hair dryer or heat gun for preflight deicing (I can’t comment about a USB powered hair dryer; never heard of such a thing).  You would have to keep the temperature down to avoid damaging or warping plastic parts eg fairings, windshields, etc.  Probably the best way to de-ice a light aircraft is either just to park it in a warm hangar overnight or park the aircraft in the sun for an hour or so prior to flight.

There are many things you can do to mitigate the risk of icing, but most involve prevention via avoidance of icing conditions.  For example, getting a good weather brief, knowing where the freezing level is, staying away from visible moisture, and finally, recognition and taking evasive action.
Pre-flight deicing liquids are not intended to prevent ice accumulation in flight.  As you noted, they will just blow off in the slip stream.  Anti-icing fluids such as TKS are very effective, but the aircraft must be equipped with a system to properly disperse it to be certified for flight into known icing conditions.
If you are not instrument rated it gets easier, because if you stay out of clouds you won’t ice up.  But if you want to fly IFR in the winter, (or any time you could be IFR in the  temperature zone where ice could form) your best method of increasing the safety margin is to arm yourself with knowledge, practice operational risk management, and exercise sound judgment to keep yourself out of icing.

In the end, for a VFR pilot, if there is any chance of running into rain in winter, it's all about the freezing level.  The criteria for use of heat anti-icing on jets for departure is visible moisture (which can be rain, snow or mist/cloud) below +5C OAT.  The pressure drop over the wings causes a small temperature reduction that eats into this margin, so it's actually less than +5C on top of the wings when you are flying in +5C free stream air, especially at lower speeds.
Due to the extreme danger of an icing encounter, this margin is probably not really enough for VFR and it would be a good idea to use +10C/5000 ft below freezing level as a planning minimum if there is any risk of a rain encounter on a trip.
You would apply this safety margin such that when you check the weather and there is any chance of an encounter with rain, you want to make sure the freezing level is 5000 ft above your planned minimum cruising level to give you at least that +10C safety margin for the entire route.  If you can't cruise at least 5000 ft below the freezing level, you have to be sure the air will be free of any visible moisture on your route.
A brief encounter with snow is not too bad, from an accumulation risk perspective, if the temperature is well below freezing and the snow is very light, but still best to avoid it because the effect on visibility is severe in anything more than very light snow and it can change from light to not so light pretty fast and it's quite frightening.  So stay away from snow.

Anti-icing fluid (a different mix of the same chemicals used for de-icing) applied to airliners is only effective at keeping ice from forming on the planes while taxiing and waiting to take off. All that fluid will be blown off the plane by the time it rotates, though. Once in the air, a plane must rely solely on its onboard de-/anti-icing systems until landing.
If a plane doesn't have the latter, then
the former won't do anything of value. If you can't stay out of icing conditions, then stay on the ground until they pass. Period.


text:
What is the meaning of the triangular markings in the A320 cabin?
Travelling in a chartered A320 from Titan Airways. Does anyone know what these triangular markings mean? They can be seen on both sides of the cabin, a few rows before and after the emergency exits.


text:
Is it required to have an alternate airport if you don't have a WAAS GPS?
I forgotten if an alternate is required if you don't have a WAAS GPS regardless of the 1-2-3 rule which states that 1 hour before and after ETA at your destination airport, the ceilings must be at least 2000' and 3 miles visibility. Must we file an alternate or is it dependent on the 1-2-3 rule? Which regulation talks about this because I can't find it.

You may use the LNAV/VNAV minimums for flight planning purposes if are have approved baro-VNAV capabilities. (even if you are non-WAAS equipped). AIM 1-1-18)

Probably worth noting that very few general aviation piston aircraft have baro-VNAV equipment installed and (my understanding is) few transport category aircraft have WAAS GPS installed.


text:
What would be the best alternative during a dead-stick approach?
(Disclaimer: I am not a pilot so my understanding of things may be really broken)
If a plane has lost engine power, has limited altitude to work with, and is upwind of a landing strip, and the pilot doesn't believe she has enough glide range to pass the appropriate runway and turn around for a landing into the wind on the full length of the runway, would it make more sense to
(a) land directly on the full length of the runway, accepting the tailwind
or
(b) pass part of the runway, turn 180, and land into the wind using only, let's say, half the runway length
Assume that an emergency has been declared, airspace and runway are all cleared, etc. In my particular scenario we're talking about a single-seat, single-engine fighter-type plane with generally poor glide ratio. I'm curious about any contributing factors.

It probably depends on the strength of the wind and how much altitude there is. My uninformed guess is that pilots would generally prefer the simpler option - i.e. no last-minute turn.

Even with a tailwind it would almost certainly be best to just land and accept possibly running off the end of the runway under control and at low speed. That's a lot safer than messing up a turn at low altitude and airspeed, and possibly stalling. But there are plenty of variables and what ifs in any scenario like this.

I have never flown a fighter-type plane, but there is a number of things common to any type when it comes to an emergency, dead-stick landing. First of all, stabilize the glide, and second, try to find ahead a reasonable place to land or crash-land. And while doing that, make a mayday call. With fast-sinking planes there's usually no time for many choices on how or where to land...

Related: Is it even remotely feasible to turnback a single engine aircraft with an engine failure?

What's wrong with landing with a tailwind?  There are a number of back-country strips where that's the only option, or the most practical one unless the wind is really strong.  Given the higher landing speeds, tailwinds would seem to be even less relevant in fighter-type aircraft than in single-engine prop planes.

Recipe for stall/spin: Start at low airspeed, add tailwind, reduce altitude to low, make tight 180° turn, bake in fuel fire for 10 min until crispy

Attempting a tight turn, while low and slow, is an almost certain recipe for disaster.
Your first option of landing with a tailwind is possibly preferable - there is no inherent danger landing with a tailwind - it'll extend your landing, and is not ideal. However, it is much safer than trying to maneuver into a position with a headwind with only part of the runway remaining. And with a short runway to start with (if that was the case) you might not have enough distance to land safely anyway.
There is a third option, with the setup you describe, which is to completly disregard the (seemingly) obvious runway close by and look for a suitable area to land in front - a field, a highway, a beach - any of the usualy places you might make an emergency landing in the case of an engine failure.
(Disclaimer: My experience is with single engine propeller aircraft, but I am fairly sure the mantra of Aviate, Navigate, Communicate applies to all aircraft types. Really, in this situation its only the aviate that is relevant)

I think the important mantra here is that in emergency poor but certain options are better than uncertain options no matter how good they might otherwise be. You only have one attempt, so choose the option that is easy.

Regarding aviate, navigate, communicate, in this context, aviate just means push down and stabilize on best glide speed, retracting flaps in the process if they were out. Then you look for suitable spot for forced landing, which is navigation. And if you are high enough, and have radar services, you may even communicate first and ask ATC for nearby runways.

@JanHudec - you're right. In the ideal you'd indeed utilize all three. That was poorly worded in my answer.

It depends on a number of factors including the aircraft type, its associated glide/descent ratio at max L/D, where the a/c in relation to the landing site, your current absolute altitude, other potential landing sites nearby, etc.  Many of these factors should have been discussed and anticipated for in the pre takeoff briefing prior to flight and is going to require some savvy ADM sometimes in order to make the right decisions.
For ASEL operations, I usually do the following pre-takeoff brief:
Loss of engine power on runway before Vr - ABORT TAKEOFF
Loss of engine, airborne, adequate rwy left - ESTABLISH BEST GLIDE, LAND STRAIGHT AHEAD ON RWY.
Loss of engine, airborne, no rwy left, 0-300 ft AGL - ESTABLISH BEST GLIDE, MAKE OFF FIELD LANDING STRAIGHT AHEAD.
Loss of engine, airborne, no rwy left, 300-600 ft AGL - ESTABLISH BEST GLIDE, SELECT BEST LANDING SITE WITHIN GLIDING DISTANCE +/- 30° FROM RWY HEADING, MAKE FORCED LANDING ON THAT SITE.
Loss of engine, airborne, no rwy left, 600-900 ft AGL - ESTABLISH BEST GLIDE, SELECT BEST LANDING SITE WITHIN GLIDING DISTANCE +/- 90° FROM RWY HEADING, MAKE FORCED LANDING ON THAT SITE.
Loss of engine, airborne, no rwy left, >1000 ft AGL - ESTABLISH BEST GLIDE, SELECT BEST LANDING SITE ANYWHERE AROUND AIRPLANE WITHIN GLIDING DISTANCE, MAKE FORCED LANDING ON THAT SITE.  NOTE: DEPARTURE AIRPORT MAY OR MAY NOT MEET THAT CRITERIA AT THIS POINT.
IF TIME AND WORKLOAD PERMIT, COMPLETE ENGINE FAILURE AND FORCED LANDING EMRGENCY CHECKLISTS.

You and I both know what all caps means on an emergency checklist, but it would be much easier to read this answer without them.


text:
How long does the gear extension/retraction takes on the ATR-42?
Which is typical time of landing gear extension in normal conditions ? I would like to know it especially for the ATR-42 but any other typical value is welcome !
Furthermore can you provide any link to data sheet for ATR-42 technical data about landing gear ?

You mean as in how long it takes for the gear to go from the up position to full down all green & vice versa?

Yes please ! That's the right question !

In this youtube video showing landing gear maintenance operations on an ATR42, I'd say about 11 seconds for both extension and retraction.
A more precise timing could be gathered from an uninterrupted cockpit video, measuring from gear lever action action to "three green" on.


text:
On a METAR, what does DSPTD mean?
KDEN is currently reporting the following METAR:
SPECI KDEN 090325Z 34031G37KT 10SM -PLRA FEW015 OVC036 08/03 A2992 RMK AO2 PK WND 35037/0325 RAB04PLB25 TS DSPTD P0000 T00830028 $
I have no idea what DSPTD stands for. My best guess is "dissipated". I have been unable to find anything online, can someone help confirm this?

That is what it means, but it should be taken with the TS too: TS DSPTD, I can't find any official source for the code though.

This is a METAR with the addition of U.S. Observations, and according to the details of the abbreviations used there is no such value as DSPTD.
I suspect you are right, that it should have been DSIPTG - which does indeed mean "dissipating". The full decode of the Remarks section of your example METAR is as follows

A02 - automated station with precipitation descriminator.
PK WND 35037/0325 - Peak wind 350 degrees at 37 knots between 03 and 25mins
RAB04 - Rain began at 04mins (You can infer the hour from the main report)
PLB25 - Ice pellets began at 25mins (Again, inferring the hour from the report)
TS DSPTD - Thunderstorms which dissipated
P0000 - Trace amount of  hourly precipitation

I should add that I'm by no means an expert at decoding this part of a METAR, I made judicious use of this page.


text:
Is there a list of accidents due to poor communication in English?
I would like a list of accidents satisfying the following criteria:

Poor communication between ATC and pilots was judged to be a major factor in the accident;
English was the language of communication between ATC and the pilots; and
The native language of the pilots and controller was the same, but not English.

I am not looking for discussion of whether using English is a good idea or not in these situations, whether its use played a role in these accidents, or whether better training in communications is needed. I just want a list of accidents where these conditions are met.
The poor communication need not necessarily have been attributed to insufficient knowledge of English.

Welcome to aviation.SE. Personally I think you question risks falling in the "shopping list" category, that is generally regarded as off-topic (and generally best suited for a discussion in chat). Stick around, gain some reputation and join us in chat! :)

Communication between ATC and flight crew is organised in phrases. That means the sentences to speak are predefined word by word. Therefore (implied that all participants use this phrases) it is more like using technical terms in your own language than speaking a foreign language.

Seems like a good question to me. Maybe there's not an immediate obvious answer to the question exactly as asked, but it would be rather pedantic to refuse to see the perfectly answerable, on-topic issue it represents

Are the current 4 VTC still valid after the edit?

While in no way an exhaustive list, SKYbrary does provide a list of accidents and serious incidents which include air-ground communication as a causal factor. The list contains example of events, and is not meant to contain every single such event.
You can find it here: http://skybrary.aero/index.php/Accident_and_Serious_Incident_Reports:_AGC
You may also want to search for communication and related terms on The Aviation Herald: http://avherald.com/h?search_term=communication&dosearch=1&search.x=0&search.y=0

@Dave You may also want to check https://aviation-safety.net